Drying of particulate materials

ABSTRACT

A tube pressure filter, for reducing the liquid content of wet, finely divided solid materials in the form of a slurry, which tube pressure filter includes a chamber of annular cross-section substantially defined by two co-axially disposed tubular bodies displaceable axially relative to one another between operative and inoperative positions and which have means which cooperate to form a seal between the adjacent ends thereof when the pressure filter is in the operative position, the outer tubular body being provided with an inlet for the introduction thereinto of a hydraulic pressure medium and the inner tubular body being provided with a plurality of apertures for the passage therethrough of filtrate, an impermeable elastic sleeve disposed in said chamber of annular cross-section and secured in liquidtight manner to the outer tubular body so as to divide said chamber into non-communicating first and second compartments of annular cross-section, and means for introducing a wet, finely divided solid material to be pressure filtered under pressure into said second compartment of annular cross-section in a manner such that said wet, finely divided solid material is charged to the bottom of said second compartment substantially uniformly around the inner tubular member so as to scour that part of the filter material supported by the lower portion of the inner tubular member. There is also provided a process for operating the pressure filter.

a "L A Unite States Patent [1 1 [111 3,756,142

Gwilliam Sept. 4, 1973 DRYING OF PARTICULATE MATERIALS [75] Inventor: Ralph Derek Gwilliam, St. Austell, [57] ABSTRACT E l d ng an A tube pressure filter, for reducing the liquid content [73] Assignee: English Clays Levering Pochin & of wet, finely divided solid materials in the form of a Company Limited, St. Austell, slurry, which tube pressure filter includes a chamber of Cornwall, England annular cross-section substantially defined by two co- [22] Filed: p 15, 1971 axially disposed tubular bodies displaceableaxially relative to one another between operative and inoperative [21] Appl. No.: 134,507 positions and which have means which cooperate to Related US. Application Data Continuation of Ser. No. 871,467, Oct. 23, 1969, abandoned, which is a continuation-in-part of Ser. No. 739,442, June 24, 1968, abandoned.

Primary ExaminerPeter Feldman Attorney-Larson, Taylor & Hinds form a seal between the adjacent ends thereof when the pressure filter is in the operative position, the outer tubular body being provided with an inlet for the introduction thereinto of a hydraulic pressure medium and the inner tubular body being provided with a plurality of apertures for the passage therethrough of filtrate, an impermeable elastic sleeve disposed in said chamber of annular cross-section and secured in liquid-tight manner to the outer tubular body so as to divide said chamber into non-communicating first and second compartments of annular cross-section, and means for introducing a wet, finely divided solid material to be pressure filtered under pressure into said second compartment of annular cross-section in a manner such that said wet, finely divided solid material is charged to the bottom of said second compartment substantially uniformly around the inner tubular member so as to scour that part of the filter material supported by the lower portion of the inner tubular member. There is also provided a process for operating the pressure filter.

29 Claims, 8 Drawing Figures PATENTED SEP 4 I973 SHEET 1 0F 7 PAIENTEnsEP 41015 3756342 SHEET 2 BF 7 PATENTEU SEP 4 I973 SHEET 3 BF 7 Y h W PATENTEDSEP 4m 3.756.142

SHEET? 0F 7 286 I k Q1 FIG.8

DRYING OF IARTICULATE MATERIALS This application is a continuation of my copending application Ser. No. 87!,467 filed Oct. 23, 1969, now abandoned, which application is a continuation-in-part of my application Ser. No.73),442 filed June 24,1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to an apparatus and a process for reducing the liquid content of wet, very finely divided solid materials, i.e., solid materials such as clays, chalk whiting, satin white and other mineral pigments comprising 20 percent or more by weight of particles smaller than 20 microns; these materials are capable of forming compressible, low permeability cakes so that the application thereto of high pressures is required to produce a low moisture content, i.e., less than 25 percent by weight moisture.

It has been known for many years that liquids may be extracted from pulpy materials and from slurries by compressible forces generated by the inflation of an elastically extensible bladder. More recently there have been described tube pressure filters wherein an impermeable, elastically extensible wall divides a chamber formed between two co-axially disposed and spaced apart tubular bodies into two noncommunicating compartments, a material to be pressure filtered being introduced into the compartment formed between one side of the elastically extensible wall and one of the tubular bodies and a hydraulic pressure medium being introduced into the compartment formed between the other side of the bladder and the other tubular body. Embodiments of such a tube pressure filter and their use for dewatering materials such as fine coal slurries are described in UK. Specification No.907,485. Each of the embodiments of a tube pressure filter described in UK. Specification No.907,485 comprises at least one chamber which is divided into two noncommunicating compartments by an impermeable elastically extensible wall, one of said compartments being defined generally by a first tubular body adapted to form a liquid-pervious wall and by the impermeable elastically extensible wall and being provided at the top of said one compartment with an inlet orifice whereby material to be pressure filtered can be charged by gravity feed to said one compartment at the top thereof and the other of said compartments being defined generally by said impermeable elastically extensible wall and by a second tubular body adapted to form a backing wall behind said elastically extensible wall and being providedwith a port whereby fluid medium can be evacuated from and fluid medium can be subsequently forced under pressure into the space behind the elastically extensible wall thereby first to stretch the major part of the elastically extensible wall up to or towards the backing wall preparatory to charging said one compartment and then to exert pressure on the charge, the elastically extensible wall being of such shape and dimensions and being so mounted between said first and second tubular bodies that when the pressure filter is not in use at least the major part of the area of the elastically extensible wall confronting the liquid-pervious wall formed by the first tubular body maintains'a position spaced both from said liquid-pervious wall and the backing wall formed by the second tubular body. It is stated in U.K.Specification No.907,485 that when using the tube pressure filters described therein high pressures of the order of L500 psig may be built up in the chamber during compression of a charge, and the tube pressure filters are stated to be suitable for dewatering mineral substances such as fine coal, which ma terial predominantly comprises particles larger than 150 microns. However, it is found that when attempts are made to use tube pressure filters constructed in the manner described in UK. Specification No.907,485 to reduce the liquid content of wet, very finely divided solid materials comprising 20 percent or more by weight of particles smaller than 20 microns, e.g., clays, satisfactory results cannot be obtained.

It is an object of the present invention to provide a tube pressure filterand a process for operating the same which can be used to reduce the water content of wet, very finely divided solid materials comprising 20 percent or more by weight of particles smaller than 20 microns.

SUMMARY OF THE INVENTION We have now found after extensive investigations that the water content of wet clays and other solid materials, such as satin white, containing at least 20 percent by weight of particles smaller than 20 microns can be reduced substantially using a tube pressure filter of a type similar to that described in U.K. Specification No.907,485 when such tube pressure filter press is constructed and operated in accordance with the present invention.

More particularly, according to one aspect of the present invention there is provided a tube pressure filter for reducing the liquid content of wet, finely divided solid materials in the form of a slurry, which tube pressure filter comprises (a) a chamber of annular cross section substantially defined by two tubular bodies which are capable of withstanding high pressures, are arranged substantially coaxially one within the other and are displaceable axially relative to one another between operative and inoperative positions and which have means which co-operate to form a seal between the adjacent ends of the two tubular bodies when the pressure filter is in the operative position, the outer tubular body being provided with an inlet for the introduction thereinto of a hydraulic pressure medium and the inner tubular body being provided with a plurality of apertures for the passage therethrough of filtrate,

( b) a filter material supported by and extending around the external wall of the inner tubular body, the filter material being arranged so as to prevent the passage through the apertures in said inner tubular body of very finely divided solid material being pressure filtered, (c) an impermeable elastic sleeve disposed in said chamber of annular cross-section and secured in liquid-tight manner to the outer tubular body so as to divide said chamber into non-communicating first and second compartments of annular cross-section, said first compartment of annular cross-section being effectively defined by the impermeable elastic sleeve and the internal wall of the outer tubular body and said second compartment of annular cross-section being effectively defined by the impermeable elastie sleeve and the external wall of the inner tubular body, (d) means for introbottom of said second compartment substantially uniformly around the inner tubular body so as to scour that part of the filter material supported by the lower portion of the inner tubular body, (e) means for removing filtrate from the interior of the inner tubular body, (f) means for displacing the tubular bodies axially relative to one another from the operative position to the inoperative position after a pressure filtering operation, and (g) means for removing the very finely divided solid material from the surface of the filter material after the filtrate has been removed from the solid material and the inner and outer tubular bodies have been axially displaced relative to one another to the inoperative position.

The tubular bodies defining said chamber of annular cross-section advantageously each comprise a cylindrical central section and end sections adapted to cooperate with the adjacent end sections of the other tubular body to form a seal when the tubular bodies are in the operative position. The means which cooperative to form a seal between the adjacent ends of the inner and outer tubular bodies when the tube pressure filter is in the operative position advantageously comprises a ring-seal, preferably an O-ring seal, mounted in the end sections of one of the tubular bodies so as to cooperate with a surface of the adjacent end sections of the other tubular body, the ring seal being made from an elastic or plastic material so as to reduce the gap between the ring seal and the surface cooperating therewith to zero. Instead of an O-ring seal there can be used, for example, a U-ring seal or a cup-ring seal. It is possible to eliminate the ring seal as long as the inner and outer tubular bodies are provided with adjacent end sections which are a close fit.

It has been found that, when used for treating materials comprising 20 percent or more by weight of particles smaller than 20 microns, the outer tubular body preferably comprises a cylindrical central section having an internal diameter not greater than 12 inches or less than 4 inches and the inner tubular body preferably comprises a cylindrical central section having an external diameter which differs from the internal diameter of the cylindrical central section of the outer tubular body by from 2 inches to 7 inches. More particularly, when the internal diameter of the cylindrical central section of the outer tubular body is 12 inches, the external diameter of the cylindrical central section of the inner tubular body preferably lies in the range to 8 inches; and when the internal diameter of the cylindrical central section of the outer tubular body is 4 inches, the external diameter of the cylindrical central section of the inner tubular body lies in the range 0.8 to 2 inches.

The filter material supported by the external wall of the inner tubular body will advantageously be a filter cloth which preferably is formed from a thermoplastic continuous filament man-made polymeric material which has been heat set, e.g., by hot calendering; such a material can have a pore size sufficiently small to prevent the finely divided solid material from passing therethrough, and the use of a continuous filament material gives the filter cloth good release properties. The thermoplastic continuous filament man-made polymeric material can be, for example, polyethylene terephthalate or nylon. The filter cloth can also be formed from a material, such as a synthetic needle cloth, a heavy weight cotton cloth or a felted woollen cloth,

which has been subjected to gentle singeing to remove projecting fibres and thus improve the release properties of the filter cloth.

In another aspect the present invention provides a process for reducing the liquid content of a slurry of a very finely divided solid material which process comprises the steps of (i) introducing the slurry of finely divided solid material under pressure into the second compartment of the tube pressure filter of the present invention whilst introducing into the first compartment of said tube pressure filter a hydraulic pressure medium having a specific gravity which differs by not more than 0.05 units from that of said slurry, the slurry of finely divided solid material being introduced into said second compartment in a manner such that said slurry is charged to the bottom of said second compartment substantially uniformly around the inner tubular body and scours that part of the filter material supported by the lower portion of the inner tubular body, (ii) raising said hydraulic pressure medium to a pressure of at least 250 psig, and preferably at least 1,000 psig, and maintaining said hydraulic pressure medium at or above said pressure for a time sufficient to effect a reduction in the liquid content of the wet, very finely divided solid material, (iii) withdrawing from said first compartment the hydraulic pressure medium, (iv) thereafter displacing the tubular bodies of the tube pressure filter axially relative to one another to the inoperative position, and (v) removing the very finely divided solid material from the surface of the filter material.

It has been found that in general the slurry of very finely divided solid material should be introduced into the second compartment of the tube pressure filter at a pressure of at least 25 psig. Good results have been obtained using a pressure of 30 psig.

In the operation of the filter press the hydraulic pressure medium is selcted so as to have a specific gravity which differs by not more than 0.05 units from the specific gravity of the feed material to be pressure filtered. This is done to ensure that the thickness of the filter cake formed on the inner tubular body from top to bottom does not vary excessively. Thus, when the pressure filter is being employed to remove water from a slurry of clay or satin white having a specific gravity of 1.150 there can be used as the hydraulic pressure medium another such slurry having a specific gravity in the range 1.100 to 1.200 or a mixture of a suitable organic liquid, e.g., glycerol, and water in the correct proportions to give the required specific gravity. In the case of a mixture of glycerol and water, a hydraulic pressure medium having a specific gravity in the range 1.100 to 1.200 can be obtained with glycerol/water mixtures in which the glycerol comprises from about 40 percent by weight to about 77 percent by weight of the mixture. The hydraulic pressure medium comprising a mixture of an organic liquid and water has the advantage that it contains no solid particles which tend to cause wear by abrasion in the hydraulic system.

Advantageously, the filter cake is removed from the filter material after a filtering operation by one or more air blasts delivered into the interior of the inner tubular body. With such a system, during the operation of the filter press the amount of material treated is preferably selected so that the thickness of the filter cake formed on the inner tubular body is not less than 0.2 inches, to ensure that it is broken by the air blasts and does not flex, and generally not more than 0.3 inches thick, to

obtain maximum throughput since it is found that a thicker cake requires a disproportionately longer operating cycle. Preferably, the filter cake is removed from the filter material by a number of short, discrete air blasts, rather than by one long blast, since the repeated increase and decrease in the diameter of the filter material coupled with the air pressure is more effective than the air pressure alone in releasing the filter cake.

The process of the present invention is particularly useful for reducing the water content of efflorescent materials such as satin white. Satin white is a calcium sulphoaluminate pigment having the formula 3CaOAl- O '3CaSO,-3 lI-I O which is used in paper coating compositions to impart high brightness and gloss and good printability to the coated paper. Satin white is prepared by interacting aluminium sulphate and slaked lime, the satin white thus formed being stored and transported as a moist paste. Thus, in one method of producing satin white a concentrated aluminium sulphate solution is added to a lime paste whereafter the reactants are mixed in a high density mixer. The amount of water used is such that the paste of satin white which is produced contains about 30 percent by weight of solids. Another method of preparing satin white, which is in general use, involves spraying a solution containing about of aluminium sulphate by weight into a slurry con-taining about 5 percent of calcium hydroxide by weight until the reaction is completed and there is formed a slurry of satin white. For best results with both methods, the reaction temperature is controlled so that the temperature of the satin white paste or slurry does not exceed about 35C. Satin white, being highly efflorescent, cannot be dried by conventional methods using elevated temperatures without driving off some of the water of crystallization, and thus destroying some of the properties which make it so desirable as a pigment in paper coating compositions, and also rendering it much more difficult to redisperse completely in water. For this reason, satin white is conventionally transported, packed either in wooden casks or in polyethylene bags protected by iron barrels, in the form of a paste which usually contains from to 30 percent by weight of dry solids. It is however expensive to pack and transport satin white in this way as a considerable weight of water must be transported with the pigment, and the cost of packaging is high. On pressure filtering, satin white forms a cake of low permeability to liquids which is compressible and I have found that the pressure filter of the present invention can be used to produce a filter cake of satin white having a solids content of more than 70 percent by weight. This represents a considerable improvement over the known pressure filters which, in general, could only reduce the water content of a slurry of satin white to about 60 percent by weight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1 shows, partly in section, one embodiment of a tube pressure filter according to the present invention;

FIG. 2 shows diagrammatically the pressure filter of FIG. I and its ancillary equipment;

FIG. 3 is an electric circuit diagram for the equipment shown in FIG. 2;

FIG. 4 is a timing diagram;

FIG. 5 is a diagram illustrating the arrangement of a fluid logic system for controlling the operation of the equipment shown in FIG. 2;

FIG. 6 shows, partly in section, another embodiment of a pressure filter according to the invention;

FIG. 7 shows partly in section, a still further embodiment of a pressure filter according to the invention; and

FIG. 8 is a plan viewof the pressure filter shown in FIG. 7.

Referring first to FIG. 1, there is shown partly in section a pressure filter which is identified generally as A and which includes an outer tubular body and an inner tubular body as described below.

The outer tubular body comprises a central cylindrical steel section 1 which has an inlet 11 for a hydraulic pressure medium, upper and lower flange portions 14 and 15 which are welded to the cylindrical section 1, upper and lower annular members 2 and 3 which are bolted to the flange portions 14 and 15 respectively, and bronze rings 4 and 5 which are secured in recesses formed in the annular members 2 and 3 respectively. Grooves 35 and 36, each containing an O-ring seal, are provided in the upper and lower flange portions 14 and 15 respectively and ensure that there is a fluid tight connection between the flange portions 14 and 15 and their respective annular members: 2 and 3. Grooves 6 and 7, each containing an O-ring seal, are formed in the bronze rings 4 and 5, respectively; the bronze rings 4 and 5 are also provided with channels 9 and 8, respectively, in which there are secured by hose clips (not shown), for example JUBILEE clips, the ends of an impermeable rubber sleeve 10 which can be dilated by the hydraulic pressure medium introduced through inlet 11. The ends of the rubber sleeve 10 are turned back to form cuffs 12 and 13.

The inner tubular body comprises a central cylindrical steel section 20 which is provided with about 1,300 uniformly distributed apertures 21, each about three thirty-seconds inch in diameter, to enable filtrate to pass therethrough, caps 22 and 23 which are screwed to the upper and lower ends of the cylindrical section 20 and which close the ends of the inner tubular section 20, and annular bronze fairings 27 and 28 which are screwed to caps 23 and 22 respectively and which have a sloping face making an angle of at least 45 with the horizontal. The rims of the caps 22 and 23 project radially beyond the cylindrical section 20 and are ground to enable there to be obtained an effective seal between the rims of caps 22 and 23 and the O-ring seals in grooves 6 and 7. The cap 22 is provided with a port which is fitted with a pipe 25 for the introduction of air at high pressure into the interior of the inner tubular member. The cap 22 is also provided with an opening through which there can be passed a siphon tube 26 for the removal of filtrate from the inner tubular member. In addition a jack 34 is connected to the cap 22 so that the inner tubular body can be displaced axially relative to outer tubular body. The projecting rim of cap 23 is provided with a port 24 through which the material to be pressure filtered can be fed under pressure into an annular duct formed by the fairing 27 and from there into the pressure filter through 104 uniformly distributed apertures 32, each three thirty-seconds inch in diameter.

It will be seen that in the operative position, as shown in FIG. I, the inner and outer tubular bodies which together comprise cylindrical sections l and 20, flange portions 14 and 15, annular members 2 and 3, bronze rings 4 and 5, caps 22 and 23, and bronze fairings 27 and 28 effectively define a chamber of annular crosssection, the chamber being divided into noncommunicating compartments X and Y by the impermeable rubber sleeve secured to rings 4 and 5.

Disposed around and supported by the tubular section 20 is a coarse weave backing cloth 30 made from SARAN (polyvinylidene chloride), and over the backing cloth there is fitted a filter cloth 29. The filter cloth 29 is formed from a hot calendered TERYLENE (polyethylene terephthalate) continuous filament, multi-ply yarn. The bottom of the filter cloth 29 is caulked at 31 with a silicone rubber compound and, in addition, the bottom few inches of the filter cloth are made impermeable by winding a polyvinyl chloride tape 33 around it; in this way the formation of filter cake near the bottom of the tube is prevented, thereby facilitating the discharge of the filter cake, and in addition leakage of the material to be filter pressed behind the filter cloth is prevented. The filter cloth is secured at each end by JUBILEE clips (not shown). The bronze fairings 27 and 28 are fitted over the JUBILEE clips securing the filter cloth and preventing the impermeable rubber sleeve coming into contact with sharp parts. The apertures 32 in bronze fairings 27 assist in the distribution of the material fed into the compartment X through port 24.

The operation of the pressure filter will now be described with reference to FIGS. 1 and 2 of the accompanying drawings. The arrangement of the pressure filter and its ancillary equipment is shown diagrammatically in FIG. 2. The inlet port 24 of the pressure filter A is connected via a conduit 64 to a pump E which feeds into the compartment X (FIG. 1) the material to be pressure filtered. This material, generally in the form of a slip having a solids content of 40 percent by weight or less is supplied to the pump B through a conduit 63 from tank F. A conduit 65 connects the inlet 11 formed in the outer tubular member of the pressure filter A to a pump B which feeds into the compartment Y (FIG. 1) the hydraulic pressure medium. The hydraulic pressure medium is stored in Tank C and is drawn from the tank by pump B through a conduit 66. The inlet 11 is also connected direct to the tank C by conduits 67 and 68 and to a vacuum pump D by conduits 67 and 67a so that the hydraulic pressure medium can be drained from the compartment Y and returned to tank C via conduit 69, the rubber sleeve 10 thereby being dilated against the wall of the outer tubular body. The various conduits are provided with valves 70, 71, 72 and 73 to enable the various ancillary equipment to be connected at the correct time.

Initially the rubber sleeve 10 is dilated against the interior wall of the outer tubular body and the compartment X is empty. A small quantity of the hydraulic pressure medium is then allowed into compartment Y between the rubber sleeve 10 and the inner wall of the outer tubular body to cause the rubber sleeve to rest against the fairing 27. A charge of the material to be pressure filtered is then fed by pump E through port 24 and apertures 32 in the fairing 27 into compartment X between the rubber sleeve 10 and the inner tubular body. This effects a scouring operation on the fairing 27, by removing any solid material remaining from a previous operation of the filter press, and thus facilitates the discharge of the filter cake. During this scouring operation, more hydraulic pressure medium is pumped at a low pressure into compartment Y. This reduces the volume of compartment X until it is completely filled with feed material. After this stage, the pressure of the hydraulic pressure medium fed into compartment Y is increased and filtration occurs. At the same time the filtrate passing into the interior of the inner tubular body through apertures 21 is extracted through siphon tube 26 (FIG. 1). When the filtration stage has finished, the supply of hydraulic pressure medium is shut off and the compartment Y is drained under vacuum. When the compartment Y has been drained and the rubber sleeve 10 has been dilated against the inner wall of the outer tubular body, the inner tubular body is lowered by means of jack 34 and the filter cake formed on the filter cloth 29 is discharged by introducing compressed air through pipe 25 behind the filter cloth at 30 psig in short blasts of onefifth of a second at approximately equal intervals for three blasts. When the discharge of the filter cake has been completed, the inner tubular body is raised to its former position and the cycle can begin again.

The operation of the cycle is initiated by the end of filtration which is sensed by a pressure drop on the inside of the inner tubular member. The pressure pump B is air operated and provides a maximum pressure of 3,000 psig and a maximum flow of 4 gallons/minute.

The correct sequence of operation of the various parts of the equipment is assured by a cam mechanism which is controlled by the electrical circuit shown in FIG. 3. The timing diagram for the operation of this circuit is shown in FIG. 4. In the electrical circuit, the power source 40 is a supply of alternating current at volts which can be brought into circuit by means of an on/off switch 41. Generally, the equipment will operate automatically but, if desired, it can be controlled manually, the selected method of operation being brought into operation by means of switch 42. When working automatically, the operation of the various pieces of equipment is controlled by switches which are operated by solenoids S. These solenoids are energised at the appropriate times by the earns 47 to 51 driven by motor 46.

The timing diagram of FIG. 4 represents a 60-second cycle which is suspended at g to permit completion of the filtration stage, the cycle starting at 12 o'clock on the diagram and proceeding clockwise. In order to suspend the rotation of the cams during the filtration stage a pressure sensing device is mounted in the inner tubular body so that when filtrate is flowing through the siphon tube 26, the inner tubular body is effectively sealed and air leaking in through a valve (not shown) at the top causes the air pressure to rise, thus opening a pressure-controlled switch 44 (FIG. 3) and stopping the motor 46 driving the cams. The pressure controlled switch 44 is over-ridden when necessary by an extra set of contacts 43 controlled by the cams.

At the start of the cycle, the cams close the switches required to introduce feed material to be pressure filtered into the compartment X and start the pressure pump B for the hydraulic pressure medium. The pressure switch 44 is overridden until the introduction of the feed material into compartment X is complete, as otherwise the cam drive would be halted as soon as the filtrate began to flow and there would be no means of stopping the supply of feed material. When filtrate ceases to flow, the air pressure in the inner tubular body falls and the cam drive is restarted, thereby stopping the pressure pump B and starting the vacuum pump D. The inner tubular body is then lowered and three blasts of air are given to dislodge the cake. At this point the pressure switch 44 is again overridden as it has been found that the air blasts cause a sufficient pressure increase to halt the cam drive. The cycle is completed by the raising of the jack 34.

The various stages in the process are identified in FIGS. 3 and 4 as follows:

a feed material to be filter pressed introduced into the filter press;

b pump for hydraulic pressure medium on;

c cam drive maintained;

d vacuum connected;

e jack down;

f air blasts for discharging filter cake;

3 cam drive off during filtration.

Instead of the cam system described above with reference to FIGS. 3 and 4, the operation of the pressure filter and its ancillary equipment can be controlled by a fluid logic system, as shown in FIG. 5. Such a system has the advantage that it senses the stage of the process which has been reached and ensures that a new stage in the cycle is not begun before the previous stage is complete thus taking into account delays due to leaks, fall-off in pump efficiency, partially blocked feed pipes etc. Moreover, the cost of such a system is lower and it is possible to have a single control unit per tube pressure filter.

The fluid logic system shown in FIG. 5 comprises three basic units the NOT unit, the NOR unit and the flip-flop unit. A NOT unit operates in such a way that if a signal, in the form of a stream of air or other fluid at relatively low pressure, is applied to the input of the unit no signal emerges from the output and vice versa. A NOR unit operates in such a way that a signal is produced at the output only if there is no incoming signal at any of the inputs, i.e., a signal applied to any one of the inputs is sufficient to cancel the emitted signal. A flip-flop unit normally has two outputs and two inputs and a signal emerges constantly from one or other of the outputs. A signal applied to one of the inputs causes the emitted signal to switch from one output to the other output, and even an input signal in the form of a short pulse is sufficient to perform this switching action. According to the usual convention for representing flip-flops a signal at one of the inputs causes the emitted signal to switch to the output imediately opposite to that input.

The area enclosed by the broken line in FIG. 5 represents the fluid logic system and the inputs from a number of sensing units are shown down the left hand side and the actions taken by a number of relay devices when a signal is or is not received are shown down the right hand sideLThe process cycle may conveniently be said to start when the filter pressing stage has just been completed and the flow of filtrate has stopped. At this stage the only signal flowing into the fluid logic system is that applied to the upper input of NOR unit 83; flipflop unit 84 is emitting a signal from its lower outlet and flip-flop unit 86 is emitting a signal from its lower, unconnected outlet. The rubber sleeve (FIG. 1) is dilatedagainst the interior wall of the outer tubular member l by the application of vacuum and the dilated position of the rubber sleeve is sensed by a suitable device which transmits a signal to NOT unit 81. NOR unit 83 now has no signal on either of its two inputs and therefore emits a signal which lowers the jack 34 and thus the inner tubular body. The lowered position of the jack 34 is sensed and a signal, which is being applied to the upper input of NOR unit 82, is interrupted with the result that a signal is now emitted by NOR unit 82 and a blast of compressed air is given to dislodge the filter cake. (In order to simplify the diagram the circuit for producing one blast of compressed air is shown. It will be appreciated that a slightly more complicated circuit could be designed to give any number of discrete blasts). The blast of compressed air is sensed by a suitable device and a pulse signal is transmitted to flip-flop 84 which switches its emitted signal from NOR units 85 to NOR units 82 and 83. The emitted signals from NOR units 82 and 83 are thus interrupted with the result that the compressed air blast is stopped and the jack 34 is raised. The raised position of the jack is then sensed and the signal to the middle input of NOR unit 85 is interrupted. As all three inlets to NOR unit 85 now carry no signal a signal is emitted which is transmitted to the upper intake of NOR unit 87 which thus no longer emits a signal so that the vacuum which retains the rubber sleeve 10 against the interior wall of the outer tubular body is released. Simultaneously the supply of feed material and hydraulic pressure medium to compartments X and Y respectively is commenced. When the compartment X is filled with feed] material a pulse signal is transmitted to flip-flop 86 so that the emitted signal is switched to the upper outlet thus switching the emitted signal from flip-flop 84 to the lower outlet, and transmitting a signal to NOR unit 85. The emitted signal from NOR unit 85 is thus interrupted with the result that the supply of feed material and of hydraulic pressure medium at low pressure is discontinued. At the same time the supply of hydraulic pressure medium at high pressure is commenced. ,When the flow of filtrate stops a sensing device interrupts the signal to NOR unit 87. NOR unit 87 now has no signal which turns on the vacuum to draw the rubber sleeve 10 back against the interior wall of the outer tubular member. The signal from flip-flop 86 is at the same time switched to the lower unconnected outlet. The circuit is thus in the same condition as it was at the beginning of the cycle.

Referring now to FIG. 6, there is shown a pressure filter which is again identified generally as A and which includes an outer tubular body and an inner tubular body. The left-hand half of FIG. 6 is an axial section; the upper right-hand part of FIG. 6 is an elevation; and the lower right-hand part of FIG. 6 is partly sectioned to show the outer tubular body in section and the inner tubular body in elevation.

The outer tubular body comprises a central, cylindrical steel section 101 which has an inlet 111 for a hydraulic pressure medium, upper and lower flange portions 114 and 115 which are welded to the cylindrical section 101, a first upper annular member 102 which is bolted to flange portion 114, a second upper annular member 142 which is sandwiched between the upper flange portion 114 and the first upper annular member 102, a first lower annular member 103 which is bolted to flange portion 115, a second lower annular member 143 which is sandwiched between the lower flange portion 115 and the first lower annular member 103, and

rings I04 and 105 which are welded to the second annular members 142 and 143 respectively and whose inner surfaces curve towards the inner wall of the cylindrical section 101. A fluid-tight connection between the flange portions 114 and 115 and their associated annular members 102, 103, 143 and 142 is ensured by providing grooves 134 and 136, each containing the O- 1 ring seal, in the upper and lower flange portions 114 and 115 respectively, and grooves 137 and 138, each containing an O-ring seal, in annular members 142 and 143 respectively. A recess 109, of the shape shown, is defined by the upper annular members 102 and 142, and a similar recess 108 is defined by the lower annular members 103 and 143. An impermeable rubber sleeve comprises a cylindrical centre piece 110 and two end pieces 112 and 113 which are moulded separately and each of which comprises a substantially cylindrical portion and an annuar beading of approximately circular cross-section. The cylindrical centre piece 110 of the rubber sleeve is secured by adhesive to the end pieces 112 and 113 so that each end of the cylindrical centre piece 110 overlaps the substantially cylindrical portion of one of the end pieces 112 and 113. The overlapping sections of the three pieces of the impermeable rubber sleeve are tapered so as to make the joints as smooth as possible. The annular headings of the end pieces 112 and 113 are trapped in the recesses 109 and 108 respectively so that the rubber sleeve can be dilated by the hydraulic pressure medium introduced through inlet 1 l 1. The curved inner surface of the rings 104 and 105 ensure that the rubber sleeve does not come into contact with any sharp edges when it is drawn back by vacuum against the inner wall of the outer tubular body.

The inner tubular body comprises a central cylindrical steel section 120, inner caps 118 and 119 which are welded to the ends of the cylindrical section 120, outer caps 122 and 123 which fastened to the inner caps 1 18 and 119 with set screws, and bronze fairings 127 and 128 which are secured to caps 122 and 123 by set screws. A groove 106 is formed in the radially projecting rim of the upper cap 122 to accommodate an O- ring seal and a similar groove 107 is formed in the radially projecting rim of the lower cap 123 also to accommodate an O-ring seal. The abutting faces of the upper cap 122 and annular member 102 and the abutting faces of the lower cap 123 and annular member 103 are ground so as to assist in the formation of a seal between said faces. The caps 122 and 118 are each provided with a port (not shown) for the introduction into the inner tubular body of air under pressure, and are also provided with openings to enable a siphon tube 126 for the removal of filtrate from the inner tubular body to be passed therethrough. In addition, a jack (not shown) is connected to the cap 122 so that the inner tubular body can be displaced axially relative to the outer tubular body. Forty-eight ducts 121 of 4; inch diameter are uniformly distributed around and extend through the rim of cap 1 l9 and 12 additional holes of V4 inch diameter are uniformly disposed about the surface of the central tubular section 120. The cap 123 is provided with a port 124 through which the material to be filter pressed can be introduced under pressure into a compartment 151 formed between the outer cap 123 and the inner cap 119. The rim of cap 123 is provided with 36 uniformly spaced ducts 132 of /32 inch diameter which extend therethrough and which are closed at their outer ends by a ring of elastomeric material 152.

It will be seen that in the operative position, as shown in FIG. 6, the inner and outer tubular bodies which together comprise cylindrical sections 101 and 120, flange portions 114 and 115, annular members 102, 103, 142 and 143, rings 104 and 105, caps 118, 119, 122 and 123, and fairings 127 and 128 effectively define a chamber of annular cross-section, the chamber being divided into non-communicating compartments X and Y by the rubber sleeve comprising pieces 110, 1 12 and 1 13.

Around the inner cylindrical section there are disposed first a sleeve of wire mesh 139, then a sleeve of a coarse weave backing cloth made of SARAN (polyvinylidene chloride) and finally a sleeve of a filter cloth 129 which is formed as a seamless tube from a hot calendered TERYLENE (polyethylene terephthalate) continuous filament, multi-ply yarn. If the wire mesh sleeve 139 is of sufficiently small mesh size it is possible to dispense with the sleeve of coarse weave backing cloth 130. A rubber ring 147, initially of rectangular cross-section, is trapped between the cap 118 and cap 122 so that when the set screws joining caps 118 and 122 are tightened the outer rim of the rubber ring 147 bulges out to form a projecting arcuate face. A corresponding groove 148 is formed in the fairing 128 to receive the projecting arcuate face. The rubber ring 147 and groove 148 co-operate to trap the sleeves of coarse weave backing cloth 130 and filter cloth 129, but the wire mesh sleeve 139 is stopped short of the rubber ring 147 and groove 148 so as not to provide a path for the leakage of liquid past the seal. A similar rubber ring 149 and groove 150 are provided between caps 119 and 123 and in fairing 127. In this embodiment of the invention it has been found unnecessary to caulk the filter cloth 129 or to tape around any part of it.

When the material to be pressure filtered is introduced under pressure through port 124 into the compartment 151 the ring 152 expands and allows the material to flow along ducts 132 into the compartment X defined by the rubber sleeve and the inner tubular body. When the material to be pressure filtered is being introduced into compartment X the hydraulic pressure medium is supplied under low pressure to compartment Y to expand the rubber sleeve towards the inner tubular body and so force the material to be treated to travel at high velocity up the sloping face of the fairings 127 and the lower part of the filter cloth 129, thus scouring them and removing any filter cake remaining from a previous cycle. During the pressing stage filtrate flows under pressure through the ducts 121 in cap 119 and collects at the bottom of the inner tubular body whence it is removed by the siphon tube 126.

The operation of the pressure filter shown in FIG. 6 can be controlled using the system described with reference to FIGS. 2, 3 and 4 or FIGS. 2 and 5.

Referring now to FIGS. 7 and 8, there is shown a pressure filter which is again identified generally as A and which includes an outer tubular body and an inner tubular body.

' The outer tubular body comprises a central, cylindrical steel section 201 which has inlets 211A and 211 B for a hydraulic pressure medium, upper and lower flange portions 214 and 215 which are welded to the cylindrical section 201, a steel annular member 202 which is secured to flange portion 214 by means of four clamps 285 and by 12 similar clamps which are not shown for simplicity (for example those manufactured by Henry Lindsay Limited and sold under the Trade Mark LINDAPTERS), an annular member 242 of high density polyethylene which is sandwiched between the upper flange portion 214 and the steel annular member 202, a steel annular member 203 which is secured to the flange portion 215 by means of sixteen clamps 291, and a second annular member 243 of high density polyethylene which is sandwiched between the lower flange portion 215 and the steel annular member 203. O-ring seals 237 and 238 are provided on the one hand between the upper flange portion 214 and annular members 202 and 242 and on the other hand between the lower flange portion 215 and annular members 203 and 243 in order to ensure a fluid-tight connection between these members.

A recess 209 of approximately circular cross-section is defined by the upper flange portion 214 and the annular member 242 and a similar recess 208 is defined by the lower flange portion 215 and the annular member 243.

Also secured to the upper flange portion of the outer cylindrical section 201 by means of the clamps 285 is a bridge assembly comprising two horizontal bars 286 and four vertical supporting columns 287. The vertical supporting columns 287 are located by means of dowel pins 288 in an annular groove 289. To the horizontal bars 286 is bolted a pneumatic cylinder 290.

An impermeable rubber sleeve comprises a cylindrical centre piece 210 and two end pieces 212 and 213. The end pieces 212 and 213 are moulded separately and each comprises a substantially cylindrical portion and an annular beading of approximately circular cross-section. The cylindrical centre piece 210 of the rubber sleeve is secured by adhesive to the end pieces 212 and 213 so that each end of the cylindrical centre pieces 210 overlaps the substantially cylindrical portion of one of the end pieces. The overlapping sections of the three pieces of the impermeable rubber sleeve are tapered so as to make the joints as smooth as possible. The annular headings of the end pieces 212 and 213 are trapped in the recesses 209 and 208 respectively thereby forming a bladder which can be dilated by the hydraulic pressure medium introduced through inlets 211A and 2118. The inlets 211A and 211B are covered with discs of wire mesh 254 and 255 respectively. The hydraulic pressure medium is supplied through a conduit 256 and the two inlets are linked by a conduit 257. Any air trapped in the compartment formed between the inner wall of the outer tubular member and the impermeable rubber sleeve may be vented through the upper inlet 211A.

The inner tubular body comprises a central cylindrical steel section 220, an upper cap 222 which is welded to the upper end of the tubular section 220, an extension piece 219 which is welded to the lower end of the tubular section 220, a lower cap 223 which is secured to the extension piece 219 by set screws, an annular member 294 of high density polyethylene which is supported on the lower cap 223, an annular fairing 228 of high density polyethylene which is secured to upper cap 222 by means of a circlip 258, and an annular fairing 227 of high density polyethylene which is supported on the annular member 294. An O-ring seal is provided to form a seal between the upper cap 222 and the fairing 228, and an O-ring seal is provided to form a seal between the extension piece 219 and the fairing 227.

The co-operating faces of the annular member 242 and fairing 228 and the co-operating faces of the annular member 243 and annular member 294 are ground to form a seal therebetween. In addition, O-ring seals are located in grooves 206 and 207 provided in annular members 242 and 243 respectively.

It will be seen that in the operative position, as shown in FIG. 7, the inner and outer tubular bodies which together comprise cylindrical sections 201 and 220, annular members 202, 203, 242 and 243, extension piece 219, ring 294, caps 222 and 223,, and fairings 228 and 227 effectively define a chamber of annular crosssection, this chamber being divided into two noncommunicating compartments X and Y by the rubber sleeve comprising pieces 210, 212 and 213.

Although not shown in FIG. 7, there are disposed around the cylindrical section 220 first a closely fitting sleeve of wire mesh, then a sleeve of a coarse weave backing cloth and finally a sleeve of a filter cloth. The cloth sleeves are shrunk to fit tightly over the sleeve of wire mesh and need no additional retaining means such as is described in connection with the embodiment shown in FIG. 1.

Material to be pressure filtered is introduced under pressure through a conduit 224, which passes through upper cap 222, into an annular compartment 251A formed in extension piece 219. The extension piece 219 is provided with 12 slots (not shown) each onefourth inch in width whereby the feed material can pass into a second annular compartment 2518. From there it passes into compartment X defined by the filter cloth, the rubber sleeve and the two fairings 228 and 227 via twentyfour slots 232 each one-fourth inch in width and the ends of which are closed by a rubber sealing ring 252 of substantially L-shaped section. When the material to be pressure filtered is introduced under pressure the ring 252 expands and allows the material to flow into the compartment. When the material to be pressure filtered is being introduced into compartment X hydraulic pressure medium is supplied at a low pressure to compartment Y to expand the rubber sleeve towards the inner tubular body and so force the feed material to travel at high velocity up the sloping face of the fairing 227 and the lower parts of the sleeve of filter cloth, thus scouring them and removing any filter cake remaining from a previous cycle. During the pressing stage, filtrate flows under pressure through a plurality of holes 221 disposed about the surface of the inner tubular body and collects in cavity 240 at the bottom of the inner tubular body from where it is removed by a siphon tube 226. An O-ring :seal 241 ensures that no liquid can pass between the cavities 251A and 240. Compressed air is admitted to the inside of the inner tubular body through a conduit 225, and the inner tubular body is moved axially relative to the outer tubular body by means of a ram which is operated by the pneumatic cylinder 290. The ram is screwed into a plate 259 of trefoil shape which transmits the motion of the ram to the upper cap 222 by means of the three vertical columns 260. A supporting plate 261 which is stifiened by four bracing fins 262 is welded to the outer tubular body to enable the whole assembly to be supported on parallel joists which are not shown.

The operation of the pressure filter shown in FIGS. 7 and 8 can be controlled using the system described with reference to FIGS. 2, 3 and 4 or FIGS. 2 and 5.

The pressure filter of the present invention is capable of operating at high pressures, e.g. at pressures greater than 1,000 psig, and the reduction of the liquid content of a very finely divided solid material which can be obtained at such pressure is illustrated by the following Table I.

TABLE I Pressure Moisture content Moisture content psig of a filler clay of a paper coating after pressure filclay after prestering sure filtering 1,000 17 21%% 2,000 14%; I8%% 3,000 13 3b l6%% 4,000 l2 l5 5,000 l l l4 6,000 109596 l3 10,000 9 l l The moisture content referred to here is the percentage of water by weight in the filter cake formed from the very finely divided solid material during the pressure filtering operation 'Ihe filler clay contained 25 percent by weight of particles smaller than 2 microns The coating clay contained 80 percent by weight of particles smaller than 2 microns The invention is further illustrated by the following example in which there was used the'tube pressure filter described above with reference to FIGS. 2, 3, 4 and 6 of the accompanying drawings.

EXAMPLE A slurry of satin white was prepared by adding a concentrated solution of aluminium sulphate to a slurry of slaked lime and mixing in a Silverson shroudedimpeller mixer. The amount of water present was such that the final solids concentration of the slurry formed was 21 percent by weight of solids which corresponds to a specific gravity of 1.100.

The slurry was divided into six portions which were each fed in turn to the tube pressure filter at a pressure of 30 psig and pressed at different pressures, using as the hydraulic pressure medium a mixture of glycerol and water having a specific gravity of 1.126. Table II below shows the solids content of the filter cake corresponding to each-pressing pressure.

TABLE II Pressing Pressure Solids Content of The three samples pressed at 500 psig, 1,000 psig and 2,000 psig each gave cakes which were hard, brittle and non-sticky, and all the cakes were readily redispersible in water.

The solids contents of the cakes were measured by calcining a sample of each cake for 3 hours at 950C. and determining the calcined weight, i.e., the weight of the calcium sulphoaluminate with no water of crystallisation. The corresponding dry weight, i.e., with no associated water but with 31 molecules of water of crystallisation, was found by dividing the calcined weight by 0.549. This assumes the formula 3CaO'Al 3CaSO -31l-I,O. The calcining temperature of 950C. is sufficient to drive off all the water of crystallisation but is not sufficient to cause the evolution of sulphur trioxide from the sulphoaluminate. In order to convert from the solids content calculated by this method to that found by drying for 4 hours at C. the solids contents found by the calcining method are multiplied by 0.66.

I claim:

I. A tube pressure filter which essen-tially comprises: (a) a pair of generally coaxial tubular bodies arranged one within the other, and adapted to be supported in a generally upright position, (b) an impermeable elastic sleeve disposed within and secured to the outer tubular body, (0) a filter element disposed around and supported by the inner tubular body, and (d) means for displacing the tubular bodies axially relative to one another between first and second positions, wherein the arrangement is such that in the first position of said tubular bodies they cooperate with each other to define a closed annular chamber which is divided into generally coaxial and non-intercommunicating inner and outer compartments by said impermeable elastic sleeve, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment, wherein the outer compartment has an inlet for a hydraulic fluid under pressure, wherein the inner compartment is provided with an inlet means for receiving a wet, particulate solid material, said inlet means being disposed at the lower end of the inner compartment and constructed such that, when the tubular bodies are supported in a generally upright position and in their first position, a wet particulate solid material to be pressure filtered can be charged to the bottom of said inner compartment through said inlet means, and wherein the tube pressure filter includes means for distributing and directing the wet particulate solid material substantially uniformly around the lower end of the inner compartment to enable scouring of at least the lower portion of the filter element.

2. A tube pressure filter as claimed in claim 1, wherein the internal wall of the inner tubular body defines a substantially closed chamber, wherein the inner tubular body includes apertures for the passage therethrough of filtrate, and wherein there is provided means for removing from the interior of the inner tubular body filtrate which has passed through the filter element and through the apertures in the inner tubular body.

3. A tube pressure filter as claimed in claim 2, wherein said means for removing filtrate from the interior of the inner tubular body comprises a syphon tube which extends through the top of said substantially closed chamber to the bottom thereof.

4. A tube pressure filter as claimed in claim 2, wherein there are provided means for removing the particulate'solid material from the surface of the filter element after said solid material has been pressure filtered and the inner and outer tubular bodies have been axially displaced relative to one another to their second position.

5. A tube pressure filter as claimed in claim 4, wherein said means for removing the particulate solid material from the surface of the filter element comprises means for producing a plurality of short, discrete air blasts within said substantially closed member.

6. A tube pressure filter as claimed in claim 1, wherein the inner tubular body comprises a central cylindrical section, and upper and lower end sections, each of which end sections includes a cap which is of larger external diameter than said central cylindrical section and a fairing mounted on or adjacent to said cap so as to extend around said central cylindrical section, the end sections of the inner tubular body being adapted to co-operate with adjacent portions of the outer tubular body to form a seal therewith when said tubular bodies are in their first position.

7. A tube pressure filter as claimed in claim 6, wherein the outer tubular body comprises a central cylindrical section, and upper and lower end sections which end sections are adapted to co-operate with the adjacent end sections of the inner tubular body to form a seal therewith when said tubular bodies are in their first position and are adapted to retain the ends of the impermeable elastic sleeve.

8. A tube pressure filter as claimed in claim 7,

wherein each of the end sections of the inner tubular body includes a ring seal which co-operates with' the adjacent end sections of the outer tubular body to form a seal therewith when said tubular bodies are in their first position.

9. A tube pressure filter as claimed in claim 7, wherein each of the end sections of the outer tubular body includes a ring seal which co-operates with the adjacent end sections of the inner tubular body to form a seal therewith when said tubular bodies are in their first position.

10. A tube pressure filter as claimed in claim 7, wherein the outer tubular body comprises a central cylindrical section having an internal diameter not greater than twelve inches and not less than four inches and wherein the inner tubular body comprises a central cylindrical section having an external diameter which is smaller than the internal diameter of the central cylindrical section of the outer tubular body by from two to seven inches.

11. A tube pressure filter as claimed in claim 6, wherein the inlet of the inner compartment comprises a plurality of apertures or ducts disposed around the lower end section of the inner tubular body in or adjacent to said fairing.

12. i A tube pressure filter as claimed in claim 6, wherein said filter element comprises a filter cloth which extends around the central cylindrical section of the inner tubular body.

13. A tube pressure filter as claimed in claim 12, wherein said filter cloth is formed from a thermoplastic continuous filament man-made polymeric material which has been heat set.

14. A tube pressure filter as claimed in claim 12, wherein the lower part of the filter cloth in the region of the fairing mounted on the cap of the lower end section is rendered impermeable.

15. A tube pressure filter as claimed in claim 12, wherein at least one of a wire mesh and a coarse weave backing cloth are-disposed between the filter cloth and the central cylindrical section of the inner tubular body.

16. A tube pressure filter as claimed in claim 7, wherein the impermeable elastic sleeve is secured to the lower end section of the outer tubular body at a position adjacent to the lower cap of the inner tubular body such that when hydraulic fluid is introduced into the outer compartment the impermeable elastic sleeve is urged towards the fairing mounted on or adjacent to the lower cap.

17. An apparatus, for use in pressure filtering a wet, particulate solid material, comprising i. a tube pressure filter which essentially comprises:

a. a pair of generally coaxial tubular bodies arranged one within the other and adapted to be supported in a generally upright position;

b. an impermeable elastic sleeve disposed within and secured to the outer tubular body;

0. a filter element disposed around and supported by the inner tubular body; and

d. means for displacing the tubular bodies axially relative to one another between first and second positions, the arrangement being such that in the first position of said tubular bodies they cooperate with each other to define a closed annular chamber which is divided into generally coaxial and non-intercommunicating inner and outer compartments by said impermeable elastic sleeve, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment, the outer compartment having an inlet for a hydraulic fluid under pressure, the inner compartment being provided with an inletfor the wet, particulate solid material which inlet is disposed at the lower end of the inner compartment and constructed so that, when the tubular bodies are supported in a generally upright position and in their first position, a wet particulate solid material to be pressure filtered can be charged to the bottom of said inner compartment through said inlet and wherein the tube pressure filter includes means for distributing and directing the wet particulate solid material substantially uniformly around the lower end of the inner com-partment to enable scouring of at least the lower portion of the filter element; and

ii. control means for controlling the supply of wet particulate solid material and hydraulic fluid to the inner and outer compartments, respectively, of the tube pressure filter when the tubular bodies are in their first position whereby, in use, the wet particulate solid material and the hydraulic fluid, under a relatively low pressure, can be supplied simultaneously to the inner and outer compartments, respectively, of the tube pressure filter until the inner compartment is filled and thereafter the pressure of the hydraulic fluid can be raised to a higher pressure sufficient to effect the desired pressure filtering.

18. An apparatus as claimed in claim 17, wherein said control means includes means for introducing a quantity of hydraulic fluid, under a relatively low pressure, into the outer compartment before the wet partie ulate solid material is fed to the inner compartment.

19. An apparatus as claimed in claim 17, wherein said control means includes means for sensing when the flow of filtrate through the filter element has substantially ceased and for actuating in sequence the evacuation of hydraulic fluid from the outer compartment, the displacement of the tubular bodies to their second position, the discharge of the solid particulate material from the filter element, and the displacement of the'tubular bodies to their first position.

20. A process for reducing the liquid content of a wet solid particulate material which process comprises the steps of (i) supporting in an upright position a tube pressure filter which essentially comprises: (a) a pair of generally coaxial tubular bodies arranged one within the other, and adapted to be supported in a generally upright position, (b) an impermeable elastic sleeve disposed within and secured to the outer tubular body, and ((1) means for displacing the tubular bodies axially relative to one another between first and second positions, wherein the arrangement is such that in the first position of said tubular bodies they cooperate with each other to define a closed annular chamber which is divided into generally coaxial and nonintercommunicating inner and outer compartments by said impermeable elastic sleeve, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment, wherein the outer compartment has an inlet for a hydraulic fluid under pressure, and wherein the inner compartment is tent of the wet, particulate solid material, (iv) withdrawing from the outer compartment the hydraulic fluid, (v) thereafter displacing the tubular bodies of the provided with an inlet means at the lower end thereof for receiving a wet, particulate solid material, said inlet means being constructed and disposed such that, when the tubular bodies are supported in a generally upright position, and in their first position, a wet particulate solid material to be pressure filtered can be charged to the bottom of said inner compartment through said inlet means substantially uniformly around the inner tubular body so as to scour at least the lower portion of the filter element; wherein, during the said supporting step, the tubular bodies of the tube pressure filter are in their first position, (ii) introducing the wet particulate solid material under pressure into the inner compartment of the tube pressure filter a hydraulic fluid having a specific gravity which differs by not more than 0.05 units from that of the wet, particulate solid material being introduced into the inner compartment in a manner such that it is charged to the bottom of said inner tubular body under a pressure sufiicient to scour that part of the inner tubular body and filter element defining the lower portion of the inner compartment, (iii) raising said hydraulic fluid to a high pressure for a time sufficient to effect a reduction in the liquid contube pressure filter axially relative to one another to their second position, and (vi) removing the particulate solid material from the surface of the filter element.

21. A process according to claim 20, wherein the wet particulate solid material is introduced into the inner compartment of the tube pressure filter at a pressure of at least 25 psig.

22. A process according to claim 21, wherein the wet particulate solid material is a slurry of a mineral pigment.

23. A process according to claim 21, wherein the wet particulate solid material is a clay slurry.

24. A process according to claim 21, wherein the wet particulate solid material is a chalk slurry.

25. A process according to claim 21, wherein the wet particulate solid material is a satin white slurry.

26. A process according to claim 22, wherein the amount of said wet, particulate solid material which is introduced into the inner compartment of the tube pressure filter is such that there is formed on the filter element a filter cake having a thickness in the range of from 0.2 to 0.3 inches and wherein said filter cake is removed from the surface of the filter element by one or more air blasts delivered against the reverse side of the filter element.

27. A process according to claim 20, wherein said hydraulic fluid comprises a mixture of an organic liquid and water.

28. A process according to claim 20, wherein a quantity of the hydraulic fluid is introduced into the outer compartment before the wet, particulate solid material is fed to the inner compartment so as to urge the impermeable elastic sleeve towards the filter element.

29. A process according to claim 20, wherein the high pressure employed to effect a reduction in the liquid content of the wet, particulate solid material is at least 1,000 psig.

I i I 

1. A tube pressure filter which essen-tially comprises: (a) a pair of generally coaxial tubular bodies arranged one within the other, and adapted to be supported in a generally upright position, (b) an impermeable elastic sleeve disposed within and secured to the outer tubular body, (c) a filter element disposed around and supported by the inner tubular body, and (d) means for displacing the tubular bodies axially relative to one another between first and second positions, wherein the arrangement is such that in the first position of said tubular bodies they cooperate with each other to define a closed annular chamber which is divided into generally coaxial and nonintercommunicating inner And outer compartments by said impermeable elastic sleeve, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment, wherein the outer compartment has an inlet for a hydraulic fluid under pressure, wherein the inner compartment is provided with an inlet means for receiving a wet, particulate solid material, said inlet means being disposed at the lower end of the inner compartment and constructed such that, when the tubular bodies are supported in a generally upright position and in their first position, a wet particulate solid material to be pressure filtered can be charged to the bottom of said inner compartment through said inlet means, and wherein the tube pressure filter includes means for distributing and directing the wet particulate solid material substantially uniformly around the lower end of the inner compartment to enable scouring of at least the lower portion of the filter element.
 2. A tube pressure filter as claimed in claim 1, wherein the internal wall of the inner tubular body defines a substantially closed chamber, wherein the inner tubular body includes apertures for the passage therethrough of filtrate, and wherein there is provided means for removing from the interior of the inner tubular body filtrate which has passed through the filter element and through the apertures in the inner tubular body.
 3. A tube pressure filter as claimed in claim 2, wherein said means for removing filtrate from the interior of the inner tubular body comprises a syphon tube which extends through the top of said substantially closed chamber to the bottom thereof.
 4. A tube pressure filter as claimed in claim 2, wherein there are provided means for removing the particulate solid material from the surface of the filter element after said solid material has been pressure filtered and the inner and outer tubular bodies have been axially displaced relative to one another to their second position.
 5. A tube pressure filter as claimed in claim 4, wherein said means for removing the particulate solid material from the surface of the filter element comprises means for producing a plurality of short, discrete air blasts within said substantially closed member.
 6. A tube pressure filter as claimed in claim 1, wherein the inner tubular body comprises a central cylindrical section, and upper and lower end sections, each of which end sections includes a cap which is of larger external diameter than said central cylindrical section and a fairing mounted on or adjacent to said cap so as to extend around said central cylindrical section, the end sections of the inner tubular body being adapted to co-operate with adjacent portions of the outer tubular body to form a seal therewith when said tubular bodies are in their first position.
 7. A tube pressure filter as claimed in claim 6, wherein the outer tubular body comprises a central cylindrical section, and upper and lower end sections which end sections are adapted to co-operate with the adjacent end sections of the inner tubular body to form a seal therewith when said tubular bodies are in their first position and are adapted to retain the ends of the impermeable elastic sleeve.
 8. A tube pressure filter as claimed in claim 7, wherein each of the end sections of the inner tubular body includes a ring seal which co-operates with the adjacent end sections of the outer tubular body to form a seal therewith when said tubular bodies are in their first position.
 9. A tube pressure filter as claimed in claim 7, wherein each of the end sections of the outer tubular body includes a ring seal which co-operates with the adjacent end sections of the inner tubular body to form a seal therewith when said tubular bodies are in their first position.
 10. A tube pressure filter as claimed in claim 7, wherein the outer tubular body comprises a central cylindrical section having an internal diameter not greater than twelve inches and noT less than four inches and wherein the inner tubular body comprises a central cylindrical section having an external diameter which is smaller than the internal diameter of the central cylindrical section of the outer tubular body by from two to seven inches.
 11. A tube pressure filter as claimed in claim 6, wherein the inlet of the inner compartment comprises a plurality of apertures or ducts disposed around the lower end section of the inner tubular body in or adjacent to said fairing.
 12. A tube pressure filter as claimed in claim 6, wherein said filter element comprises a filter cloth which extends around the central cylindrical section of the inner tubular body.
 13. A tube pressure filter as claimed in claim 12, wherein said filter cloth is formed from a thermoplastic continuous filament man-made polymeric material which has been heat set.
 14. A tube pressure filter as claimed in claim 12, wherein the lower part of the filter cloth in the region of the fairing mounted on the cap of the lower end section is rendered impermeable.
 15. A tube pressure filter as claimed in claim 12, wherein at least one of a wire mesh and a coarse weave backing cloth are disposed between the filter cloth and the central cylindrical section of the inner tubular body.
 16. A tube pressure filter as claimed in claim 7, wherein the impermeable elastic sleeve is secured to the lower end section of the outer tubular body at a position adjacent to the lower cap of the inner tubular body such that when hydraulic fluid is introduced into the outer compartment the impermeable elastic sleeve is urged towards the fairing mounted on or adjacent to the lower cap.
 17. An apparatus, for use in pressure filtering a wet, particulate solid material, comprising i. a tube pressure filter which essentially comprises: a. a pair of generally coaxial tubular bodies arranged one within the other and adapted to be supported in a generally upright position; b. an impermeable elastic sleeve disposed within and secured to the outer tubular body; c. a filter element disposed around and supported by the inner tubular body; and d. means for displacing the tubular bodies axially relative to one another between first and second positions, the arrangement being such that in the first position of said tubular bodies they co-operate with each other to define a closed annular chamber which is divided into generally coaxial and non-intercommunicating inner and outer compartments by said impermeable elastic sleeve, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment, the outer compartment having an inlet for a hydraulic fluid under pressure, the inner compartment being provided with an inlet for the wet, particulate solid material which inlet is disposed at the lower end of the inner compartment and constructed so that, when the tubular bodies are supported in a generally upright position and in their first position, a wet particulate solid material to be pressure filtered can be charged to the bottom of said inner compartment through said inlet and wherein the tube pressure filter includes means for distribut-ing and directing the wet particulate solid mate-rial substantially uniformly around the lower end of the inner com-partment to enable scouring of at least the lower portion of the filter element; and ii. control means for controlling the supply of wet particulate solid material and hydraulic fluid to the inner and outer compartments, respectively, of the tube pressure filter when the tubular bodies are in their first position whereby, in use, the wet particulate solid material and the hydraulic fluid, under a relatively low pressure, can be supplied simultaneously to the inner and outer compartments, respectively, of the tube pressure filter until the inner compartment is filled and thereafter the pressure of the hydraulic fluid can be raised to a higher pressure sufficient tO effect the desired pressure filtering.
 18. An apparatus as claimed in claim 17, wherein said control means includes means for introducing a quantity of hydraulic fluid, under a relatively low pressure, into the outer compartment before the wet particulate solid material is fed to the inner compartment.
 19. An apparatus as claimed in claim 17, wherein said control means includes means for sensing when the flow of filtrate through the filter element has substantially ceased and for actuating in sequence the evacuation of hydraulic fluid from the outer compartment, the displacement of the tubular bodies to their second position, the discharge of the solid particulate material from the filter element, and the displacement of the tubular bodies to their first position.
 20. A process for reducing the liquid content of a wet solid particulate material which process comprises the steps of (i) supporting in an upright position a tube pressure filter which essentially comprises: (a) a pair of generally coaxial tubular bodies arranged one within the other, and adapted to be supported in a generally upright position, (b) an impermeable elastic sleeve disposed within and secured to the outer tubular body, and (d) means for displacing the tubular bodies axially relative to one another between first and second positions, wherein the arrangement is such that in the first position of said tubular bodies they cooperate with each other to define a closed annular chamber which is divided into generally coaxial and non-intercommunicating inner and outer compartments by said impermeable elastic sleeve, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment, wherein the outer compartment has an inlet for a hydraulic fluid under pressure, and wherein the inner compartment is provided with an inlet means at the lower end thereof for receiving a wet, particulate solid material, said inlet means being constructed and disposed such that, when the tubular bodies are supported in a generally upright position, and in their first position, a wet particulate solid material to be pressure filtered can be charged to the bottom of said inner compartment through said inlet means substantially uniformly around the inner tubular body so as to scour at least the lower portion of the filter element; wherein, during the said supporting step, the tubular bodies of the tube pressure filter are in their first position, (ii) introducing the wet particulate solid material under pressure into the inner compartment of the tube pressure filter a hydraulic fluid having a specific gravity which differs by not more than 0.05 units from that of the wet, particulate solid material being introduced into the inner compartment in a manner such that it is charged to the bottom of said inner tubular body under a pressure sufficient to scour that part of the inner tubular body and filter element defining the lower portion of the inner compartment, (iii) raising said hydraulic fluid to a high pressure for a time sufficient to effect a reduction in the liquid content of the wet, particulate solid material, (iv) withdrawing from the outer compartment the hydraulic fluid, (v) thereafter displacing the tubular bodies of the tube pressure filter axially relative to one another to their second position, and (vi) removing the particulate solid material from the surface of the filter element.
 21. A process according to claim 20, wherein the wet particulate solid material is introduced into the inner compartment of the tube pressure filter at a pressure of at least 25 psig.
 22. A process according to claim 21, wherein the wet particulate solid material is a slurry of a mineral pigment.
 23. A process according to claim 21, wherein the wet particulate solid material is a clay slurry.
 24. A process according to claim 21, wherein the wet particulate solid material is a chalk slurry.
 25. A proceSs according to claim 21, wherein the wet particulate solid material is a satin white slurry.
 26. A process according to claim 22, wherein the amount of said wet, particulate solid material which is introduced into the inner compartment of the tube pressure filter is such that there is formed on the filter element a filter cake having a thickness in the range of from 0.2 to 0.3 inches and wherein said filter cake is removed from the surface of the filter element by one or more air blasts delivered against the reverse side of the filter element.
 27. A process according to claim 20, wherein said hydraulic fluid comprises a mixture of an organic liquid and water.
 28. A process according to claim 20, wherein a quantity of the hydraulic fluid is introduced into the outer compartment before the wet, particulate solid material is fed to the inner compartment so as to urge the impermeable elastic sleeve towards the filter element.
 29. A process according to claim 20, wherein the high pressure employed to effect a reduction in the liquid content of the wet, particulate solid material is at least 1,000 psig. 